1. Technical Field
The present invention relates in general to cooling systems for electronic devices and, in particular, to the monitoring of cooling apparatus. More particularly, the present invention relates to a multiple fan sensing circuit and a method for monitoring multiple cooling fans utilizing a single sense pin.
2. Description of the Related Art
Integrated circuits and other electrical devices generally have rated operating temperature ranges. Within these operating ranges, the devices behave according to specified requirements. Outside of the rated operating range, the response characteristics of the circuits and devices can vary from the specified requirements. At elevated temperatures, it is known for integrated circuits and other electrical devices to fail or burn out or otherwise become defective. Accordingly, it is desirable to maintain circuits and devices within their rated operating temperature ranges.
In a computer system, continued operation of an electronic device leads to the generation of heat. In some instances, albeit rare, ambient air is sufficient to provide cooling to maintain the circuit or device within the desired operating temperature range. However, some circuits or components generate enough heat to require affirmative cooling from a cooling fan. Typically, computers have included a cooling fan inside the computer housing to prevent overheating caused by the normal operation of the computer. Also, it not uncommon for a computer system, such as a server system, to utilize more than one cooling fan to maintain a specified operating temperature.
Computer systems must monitor their cooling fans to verify that the fans are powered on and rotating at a predetermined speed to maintain a desired thermal condition that precludes accelerated failures of electronic devices utilized in the computer systems. Typically, each cooling fan generates a xe2x80x9cfeedbackxe2x80x9d signal that provides information, such as rotational speed. A monitoring processor, typically a system processor, receives this feedback signal at a fan sense pin. As additional fans are added to a system, e.g., to compensate for additional electronic devices due to system upgrades, such as faster and larger disk drives, existing hardware, e.g., system I/O (Input/Output) planar boards, and/or system firmware must also be xe2x80x9cupgradedxe2x80x9d to accommodate the additional fans feedback signals. In the case of the system I/O planar board, additional inputs on the I/O board are required for the additional feedback signals. Additionally, the firmware monitoring the status of the fan must also be modified to account for the additional signal inputs. In either of the above described situations, a system upgrade to install additional fans can be time consuming and costly.
Accordingly, what is needed in the art is an improved method for installing additional fans to a system that mitigates the limitations discussed above. More particularly, what is needed in the art is a method for adding fans to a system that does not require additional hardware and/or firmware changes.
It is therefore an object of the invention to provide an improved cooling system.
It is another object of the invention to provide a multiple fan sensing circuit and a method of operation thereof.
To achieve the foregoing objects, and in accordance with the invention as embodied and broadly described herein, a multiple fan sensing circuit for use with a single fan sense input is disclosed. The multiple fan sensing circuit includes a logic circuit, coupled to the fan sense input, that combines feedback signals from a first fan and a second fan. The first fan generates a tach signal indicative of the first fan operation and the second fan, e.g., a stuck rotor type, generates either an ON or OFF signal indicative of the second fan operation. In a related embodiment, the second fan generates a logic low signal in response to a failure in the second fan. In an advantageous embodiment, the logic circuit is a connector and a logic low level in the combined operational signal indicates a failed fan.
The present invention recognizes that as additional fans are added to a system, the number of fan sense pins available for monitoring fan status and operation becomes a limiting factor. Typically, a system architecture only provides a limited number of fan sense lines. As soon as the number of fans employed in the system exceed the number the number of fan sense lines, the system cannot monitor and ensure that all the fans are operational, e.g., powered on and rotating at the appropriate speed, to maintain a desired thermal condition. Furthermore, the additional fans would also require that existing hardware, such as system I/O planar circuit boards be replaced or modified to accommodate the additional feedback signals from the additional fans. The additional fans may also necessitate replacing or modifying the system firmware to account for the additional fans. The present invention overcomes the above discussed problem of replacing/modifying hardware and/or firmware to accommodate additional fans by disclosing a novel multiple fan sensing circuit that allows a single sense line to monitor more than one fan utilizing existing fan monitoring hardware and firmware.
In another aspect of the present invention, an upgradeable fan circuit for use with a cooling system having a first fan that provides a tach feedback signal through a feedback connector is disclosed. The upgradeable fan circuit includes an auxiliary fan that generates an ON or OFF feedback signal indicative of the auxiliary fan operation. The upgradeable fan circuit also includes a first connector coupled to the feedback connector, and a second connector coupled to the auxiliary fan and the first connector that combines the tach feedback signal from the first fan with the feedback signal from the auxiliary fan and provides the combined feedback signal to a fan sense input.
The foregoing description has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject matter of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.